1. Field of the Invention
The present invention relates to Venetian blinds and, more specifically, to a lift cord concealable Venetian blind lift control mechanism for use in a Venetian blind for lifting control that keeps the lift cords from sight and from reach of children.
2. Description of the Related Art
A regular Venetian blind is generally comprised of a top rail, a bottom rail, a plurality of slats arranged in parallel between the top rail and the bottom rail, a lift control mechanism for controlling lifting and positioning of the bottom rail to adjust the extending area of the Venetian blind, and a tilting control mechanism for controlling the tiling angle of the slats to regulate the light. The lift control mechanism comprises a lift cord suspended from the top rail at one side for operation by hand to control the elevation of the bottom rail. Because the lift cord is exposed to the outside, it destroys the sense of beauty of the Venetian blind. Further, because a child can easily reach the exposed lift cord, an accident may occur when a child pulling the lift cord for fun.
U.S. Pat. No. 6,024,154 discloses a Venetian blind lift control mechanism, which keeps the lift cords from sight. It is to be noted that the marked numbers described hereunder are quoted directly from U.S. Pat. No. 6,024,154. According to this design, the Venetian blind lift control mechanism comprises a T-shaped retaining member 51 mounted inside the bottom rail 22 on the middle, two lift cord take-up members 32 respectively pivoted to the T-shaped retaining member 51 at two sides and adapted to wind up the lift cords 41 of the Venetian blind, and two spring means 33 adapted to provide a torsional force to the lift cord take-up members 32 respectively. The T-shaped retaining member 51 has a rack 512, which is forced by springs 513 into engagement with engagement means 322 of the lift cord take-up members 32 to stop the lift cord take-up members 32 from rotary motion, keeping the bottom rail 22 at the desired height. When the user pressed the T-shaped retaining member 51, the lift cord take-up members 32 are released for free rotation. At this time, the user can lift the bottom rail 22 for enabling the torsional force of the spring means 33 to force the lift cord take-up members 32 to wind up the lift cords 41, or pull the bottom rail 22 downward against the torsional force of the spring means 33, so as to adjust the bottom rail 22 to the desired height. This Venetian blind lift control mechanism is complicated, resulting in high manufacturing cost and complicated installation procedure. Further, when adjusting the elevation of the bottom rail, the user has to press the T-shaped retaining member with one hand and move the bottom rail with the other hand.
The present invention has been accomplished to provide a lift cord concealable Venetian blind lift control mechanism, which eliminates the aforesaid drawbacks. It is the main object of the present invention to provide a lift cord concealable Venetian blind lift control mechanism, which keeps the lift cords of the Venetian blind from sight and out of reach of children. It is another object of the present invention to provide a lift cord concealable Venetian blind lift control mechanism, which is easy to operation. It is still another object of the present invention to provide a lift cord concealable Venetian blind lift control mechanism, which is simple and inexpensive to manufacture. To achieve these objects of the present invention, the lift cord concealable Venetian blind lift control mechanism is installed in a Venetian blind, which comprises a top rail, a bottom rail, a plurality of slats arranged in parallel between the top rail and the bottom rail, and two lift cords vertically inserted through the slats and arranged in parallel. The lift cord concealable Venetian blind lift control mechanism comprises a base installed in one of the top and bottom rails of the Venetian blind, the base comprising two screw rods axially horizontally aligned in a line between the lift cords, an axle hole axially extended through the screw rods; a revolving rod inserted through the axle hole of the base for free rotation relative to the base, the revolving rod having two distal ends respectively extended out of the screw rods; a spring member mounted in the base and adapted to impart a torsional force to the revolving rod; and two bobbins respectively threaded onto the screw rods and coupled to the ends of the revolving rod for synchronous rotation with said revolving rod and for axial movement relative to the screw rods to wind up/let off the lift cords upon forward/backward rotation of the revolving rod.